The SurfaceTool is used to construct a Mesh by specifying vertex attributes individually. It can be used to construct a Mesh from a script. All properties except indices need to be added before calling add_vertex. For example, to add vertex colors and UVs:

The above SurfaceTool now contains one vertex of a triangle which has a UV coordinate and a specified Color. If another vertex were added without calling add_uv or add_color, then the last values would be used.

Vertex attributes must be passed before calling add_vertex. Failure to do so will result in an error when committing the vertex information to a mesh.

Additionally, the attributes used before the first vertex is added determine the format of the mesh. For example, if you only add UVs to the first vertex, you cannot add color to any of the subsequent vertices.